Each year, the NHS uses and replaces hundreds of thousands of hip, knee and spinal implants, with the average life of these implants just 15 years.

With the recent £20bn pledge from the government to boost the NHS, the UK should be looking at other ways the health service could save money.

3D printed metal implants could last longer than regular implants, be more durable and potentially save the medical industry money it so desperately needs.

Ahead of him receiving the prestigious Royal Academy of Engineering’s Silver Medal, The Manufacturer sat down with Chris Sutcliffe, Professor at the University of Liverpool, to talk about his 20-year career in the additive manufacturing of orthopedic implants and just how “additive manufacturingwill revolutionise the whole orthopedic implant industry”, as he says.

Sutcliffe, who also works as an R&D director for Renishaw, explained his research work with US implant giant Stryker Orthopaedics – a US-based company leading in the medtech industry, with global sales $12.4bn.

He said: “All 3D printing relies on the simplification of a 3D problem to a 2D one, this simplification is the key to creating really complex 3D structures by decomposing the single 3D problem to a sequence of 2D ones.”

He explained that the implants developed are made with a 3D porous surface, which – to the human eye – resembles the structure of bone, adding: “Our implants don’t need screws or adhesives and both the initial fixation straight after implantation and the long term stability are fantastic.”

Why are they different?

The bone is a living material and it remodels itself in the presence of stress, this is why our skeletons are efficient structures with material distributed only where it is needed.

Sutcliffe said: “If you implant a stiff strong material, as in the case of a standard implant, loads [forces] are distributed to the implant and the surrounding bone will remodel itself leading to loosening of the implant.”

This initial loosening leads to a wearing of the implant and further loosening which will eventually result in failure.

Sutcliffe explained the difference between traditional and AM implants: “The 3D printed implant’s surface results in a smooth load transfer between the device and the skeleton, because the 3D porous surface becomes filled with living bone.

“Similarly because the porous surface also has a lower modulus than a standard implant, the stiffness difference between the metal and the bone is reduced.”

The surface enables the AM implants to fit “perfectly” to the bone, and make an effective biological integration.

He explained that the difference is the material, which can only be achieved by AM: “With AM implants, we generally immediately think of custom designed implants because we can create the customised CAD data required from CT scans.

“If you were making a mandibular implant in, say the left jaw, you don’t want to have a standard implant, you want it to match the right side. Or if you had a serious injury where the skeleton had been really broken, you can’t repair that with a standard implant.”

When a customised implant is fitted, the bone will remodel itself to that particular implant. He added: “There is very little point in creating a customised implant for each and every case unless you are treating a particularly bad injury, or something that requires it to be in some way body matching – that is often the point that people miss.”

Sutcliffe explained that there is a market for customised implants, but there is a “much larger market for sized implants, it’s like going and buying your shoes, they come in left and right and sizes 1-25.

“They are generally stocked in hospitals so the surgeon can choose which to use at will, allowing sufficient granularity to treatment to ensure that the fit is excellent.”

How does the manufacturing process work?

The 3D printed implants rely on data inputs to AM machines, with the process started by creating a complex CAD model, this – according to Sutcliffe – is the tricky bit.

The data from the CAD model gets taken via an interface into the build preparation software, and then that data is prepared for the machine. It then gets sent to the machine and the manufacturing process starts.

During the manufacturing process, large amounts of data are collected from sensors on the machine. At Renishaw, Sutcliffe said one terabyte of data is collected each day.

Then the implant is produced and the team can use this data to conclude whether it is useful for future production. Sutcliffe explained it is not yet fully automated, but that is the goal.

Manufacturing opportunities and challenges

The cost of making these implants is higher than regular implants, but Sutcliffe explained: “That goes hand in hand with machine speed, Renishaw are working really hard to make our machines go faster and faster, we are also making them easier to use and the turnaround interaction with machines as short as possible.”

He added: “The quality of the material coming off of our latest machines at Renishaw is astounding.”

He also described AM as an “enabling technology that allows the freedom that engineers have always wanted” but have been restricted by the manufacturing process previously.

He added: “There are still some constraints with the AM technology, and it is quite difficult to do the design for the process. But once you have got that right for a particular family of products, you can really progress rapidly.”

Veterinary implants

Fusion Implants is a venture that Chris and his graduated PhD students run, the company produces AM implants for veterinary surgeries.

He explained that they have just developed an AM plate specifically tailored for springer spaniels as they have a predisposition to elbow injuries.

Sutcliffe said: “They have got a congenital defect in their elbow, the condyles don’t always form properly and you end up with a void, and they quite regularly break one of the condyle off, it is a pretty horrific injury.

“We have taken a raft of CT scans of the dogs, and then we extracted features from the CT scans that allow us produce a custom fitted implant for a type of dog.

“We offer several different sizes for this, and those cover the whole range of springer spaniels. It is all about using the data properly.”

The bone is a living form and will bind to the implant that is fitted, but the porous structure enables this fusion to be more effective – image courtesy of Stryker Orthopaedics.

The future for 3D printed implants?

People typically get implants around the average age of 70, and often these are fitted after years of pain.

The current implants used wear out and need to be replaced after around 15 years, this means surgeons want to delay the procedure for as long as possible to ensure that if the implant needs to be revised it can be.

Sutcliffe said of the AM implants: “What this technology we believe will do, is allow you to have an earlier initial implantation.

“It would alleviate suffering because of that and it’ll also, we think, reduce the cost further along on health services, because they won’t have to do as many revisions.

“The implants might be slightly more costly, but there will be less of them used over time.”

Implant performance is recorded on medical registers, and this essentially show the outcomes of one implant against another to allow patient and surgeon to make informed choices as to which device to choose.

Sutcliffe explained that AM implants haven’t been around for long enough to be acknowledged on the registers yet, but what early stage data is showing is that the implants perform just as well as current ones on the market, “but they will eventually perform much better,” he concluded.